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Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Noh, S.*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2080 - 2084, 2015/10
Times Cited Count：14 Percentile：71.37(Nuclear Science & Technology)The vacuum plasma spray (VPS) technique has been investigated as the most practical method to form Tungsten (W) layer as a plasma facing material in fusion devices. The issues are the thermal conductivity and the strength of VPS-W, i.e., the thermal conductivity of VPS-W were significantly lower than that of the bulk W, and the hardness of VPS-W is much less than that of the bulk W. These are mainly caused by the porous structure of VPS-W. In order to solve these issues, friction stir processing (FPS) was applied on VPS-W in this study. It was suggested that FSP can contribute to significant improvement both in mechanical and thermal properties of VPS-W coating.
Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2054 - 2057, 2015/10
Times Cited Count：1 Percentile：8.67(Nuclear Science & Technology)Reduced activation ferritic/martensitic steel, as typified by F82H, is a promising candidate for structural material of DEMO fusion reactors. To prevent plasma sputtering, tungsten (W) coating was essentially required. This study aims to examine the irradiation effects on hardness and microstructure of vacuum-plasma-spray coated W-F82H steel, with a special emphasis on the impacts of grain-refining induced by frictional stir processing (FSP). It was revealed that the hardness of the VPS-FSP W after ion-irradiation to 5.4 dpa at 800
C were not remarkably changed, where bulk W usually exhibited significant irradiation hardening.
Nozawa, Takashi; Ozawa, Kazumi; Asakura, Yuki*; Koyama, Akira*; Tanigawa, Hiroyasu
Journal of Nuclear Materials, 455(1-3), p.549 - 553, 2014/12
Times Cited Count：17 Percentile：74.92(Materials Science, Multidisciplinary)SiC/SiC composite is a promising candidate material of fusion DEMO reactor. This paper aims to identify its damage tolerance and strength anisotropy by various characterization techniques such as acoustic emission (AE) monitoring, electrical resistivity (ER) measurement, and digital image correlation (DIC). The AE results identified that damage accumulation initiated prior to the proportional limit stress (PLS) by both tensile and compressive loadings for 2D composites. The preliminary AE waveform analysis implied that this AE detect strength corresponds to initiation of micro-cracking but the stress-strain curve shows further linearity due to the strong interfacial friction. Then fiber sliding occurred near the PLS, followed by the non-linearlity of the curve. The preliminary tensile test results using a notched specimen also suggest notch insensitivity of the composites in any loading directions. The detailed failure mechanism will eventually be discussed with ER and DIC results.
Nozawa, Takashi; Kim, S.*; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 89(7-8), p.1723 - 1727, 2014/10
Times Cited Count：12 Percentile：66.18(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate material for the advanced fusion DEMO blanket. For the design of the DEMO, the stability of high-temperature strength of SiC/SiC composites needs to be identified. Additionally, strength anisotropy needs to be clarified because of its unique fabric architecture. This study therefore aims to evaluate mechanical properties by various modes at elevated temperatures, eventually providing a stress envelope for the design. A P/W Tyranno-SA3 fiber reinforced CVI SiC matrix composite with multilayered SiC/PyC interface was evaluated in this study. Tensile and compressive tests were conducted by the SSTT specifically arranged for the high-temperature use. In-plane shear properties were contrarily estimated by the off-axial tensile method assuming that the mixed mode failure criterion is valid for composites. All tests were performed in vacuum. The preliminary test results indicate no degradation of both proportional limit stress (PLS) and the ultimate tensile strength at temperatures below 1000C. Similarly, no significant degradation of high-temperature compressive and in-plane shear properties were identified, finally providing the stress envelope at elevated temperatures for the design.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 88(9-10), p.2543 - 2546, 2013/10
Times Cited Count：16 Percentile：73.38(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate for a fusion DEMO blanket. Due to the inherent quasi-ductile failure of composites, determining failure scenario for this class of composites is undoubtedly important to develop design codes in practical use of them. This study aims to evaluate the failure behavior of the quasi-ductile SiC/SiC composites to provide a strength map. For this purpose, detailed tensile, compressive and in-plane shear failure behaviors were evaluated by the acoustic emission (AE) technique. The AE results distinguished damage accumulation processes by wavelet analysis. Of particular emphasis is that matrix cracking occurred prior to the PLS by both tensile and compressive loadings because the rough-surface of SiC fibers resulted in the strong frictional stress at the fiber/matrix (F/M) interface. In this paper, an updated failure envelope will be provided by referring the actual matrix cracking stresses as more realistic and reasonable failure criteria.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Ceramic Materials for Energy Applications II, p.95 - 110, 2012/11
This study aims to identify failure behavior of SiC/SiC composites by varied test modes. For this purpose, acoustic emission (AE) was applied to detect composites' failure. Tensile and compressive tests were conducted for a plain-weave (P/W) chemical vapor infiltration (CVI) composite. Various loading angles were applied to discuss an anisotropic issue. AE results distinguished damage accumulation processes in axial and off-axial loading cases. Specifically, test results indicated a clear difference of damage density between tensile and compressive tests. This study also classified the characteristic failure modes by separately discussing localized variations of power within a time series by wavelet analysis.
Nozawa, Takashi; Ozawa, Kazumi; Choi, Y.-B.*; Koyama, Akira*; Tanigawa, Hiroyasu
Fusion Engineering and Design, 87(5-6), p.803 - 807, 2012/08
Times Cited Count：33 Percentile：89.95(Nuclear Science & Technology)A SiC/SiC composite is a candidate material for a demonstration fusion power reactor. Considering the inherent anisotropy of composites with variety of fabric architecture is required to precisely predict axial and off-axial mechanical properties by various failure modes. This study evaluated crack propagation behavior by the various modes to provide a strength anisotropy map and we discussed a methodology to analytically predict this trend. The strength anisotropy maps identified for various fabric orientations clearly indicate that the composites failed by the mixed modes. Specifically, due to the axial anisotropy, five individual modes such as tensile/compressive strengths in the axial/transverse directions, respectively, as well as the in-plane shear strength, are identified to be essential. In this study, with the analytical criterion based on the Tsai-Wu model, the strength anisotropy could satisfactorily be described.
Matsui, Yoshinori; Takahashi, Hiroyuki; Yamamoto, Masaya; Nakata, Masahito; Yoshitake, Tsunemitsu; Abe, Kazuyuki; Yoshikawa, Katsunori; Iwamatsu, Shigemi; Ishikawa, Kazuyoshi; Kikuchi, Taiji; et al.
JAEA-Technology 2009-072, 144 Pages, 2010/03
JAEA-Technology-2009-072.pdf:45.01MB
"R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant" was carried out from FY2006 in a fund of a trust enterprise of the Ministry of Education, Culture, Sports, Science and Technology. The coupled irradiations or single irradiation by JOYO fast reactor and JRR-3 thermal reactor were performed for about two years. The irradiation specimens are very important materials to establish of "Evaluation of Irradiation Damage Indicator" in this research. For the acquisition of the examination specimens irradiated by the JOYO and JRR-3, we summarized about the overall plan, the work process and the results for the study to utilize these reactors and some facilities of hot laboratory (WASTEF, JMTR-HL, MMF and FMF) of the Oarai Research-and-Development Center and the Nuclear Science Research Institute in the Japan Atomic Energy Agency.
Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*
no journal, ,
no abstracts in English
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. In order to design a damage tolerant composite, fiber/matrix interfacial properties with and without irradiation effects should be thoroughly and systematically understood. For this purpose an approach using model composites is considered to be suitable. This study examines the effects of different fibers and interphases on tensile and interfacial properties of non-irradiated SiC/SiC minicomposites which have high crystalline and near stoichiometric SiC fibers. As a result of the tensile unloading-reloading cyclic tests, following analysis of the hysteresis loops, and the single fiber push-out tests, (1) fiber surface roughness can significantly affect interfacial sliding stress and hence each tensile characteristic such as tensile strength/strain and hysteresis loop width, and (2) interphase thickness would also influence the interfacial and tensile properties.
Nozawa, Takashi; Nakata, Toshiya; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
no abstracts in English
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu; Kato, Yutai*; Snead, L. L.*
no journal, ,
A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. Unloading-reloading cyclic tensile tests were conducted to estimate interfacial properties for unidirectional SiC/SiC minicomposites reinforced by Hi-Nicalon Type-S (HNLS) or Tyranno-SA3 SiC fibers via CVI process were conducted. The interfacial properties were also evaluated by fiber push-out test. According to these results, it is implied that both fiber surface roughness and interfacial layter thickness can impact the tensile and interfacial properties.
Ozawa, Kazumi; Nozawa, Takashi; Uto, Hiroyasu; Someya, Yoji; Tanigawa, Hiroyasu; Tobita, Kenji
no journal, ,
A silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate material for the advanced fusion DEMO blanket. Two options are considered for the use of the composites in the DEMO design: materials functionally used such as a flow channel insert in Pb-Li liquid cooling system, and ones used as a part of structural components. This paper primarily aims (1) to show examples of Japanese blanket concepts, such as SlimCS and VECTOR, which SiC materials are considered to be used, comparing with other US or EU designs, and (2) to summarize/organize the neutron/ion irradiated swelling data currently obtained for the target temperature ranges of mainly 
700C for functional use and 1000C for structural, with a strong emphasis on the effects of helium on swelling of SiC.
Ozawa, Kazumi; Nozawa, Takashi; Toyoshima, Kazuoki*; Tanigawa, Hiroyasu; Hinoki, Tatsuya*
no journal, ,
An advanced SiC/SiC composite is a promising candidate material for fusion DEMO blanket. Current study preliminarily aims to examine tensile deformation behavior of unirradiated advanced SiC/SiC composites tested at high temperatures. In rupture tests being concurrently conducted at 1000C in vaccum, it was revealed that the plain-woven CVI-SiC matrix composite reinforced with Tyranno-SA3 fibers did not fail at 174 MPa (equivalent to 130% of PLS at 1000C) for 1986 hours. Presently there was no negative sign of the notch effects, implying their good rupture property at certain conditions of concern.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
A SiC/SiC composite is a promising candidate material for various engineering applications. For the practical design of composite components, the detailed failure mechanism need to be clarified since composites exhibit unique quasi-ductility in fracture. Focusing on the surface flaw issue, identifying notch sensitivity is essential to judge damage tolerance of composite materials. To date, it is convinced that composites with moderate fiber/matrix interface are generally notch insensitive. However, recent work by the authors claimed indicative notch sensitivity of advanced SiC/SiC composites by the off-axial tensile loading case. This study aims to identify the detailed damage accumulation behavior of this class of composites to fully understand their notch sensitivity. For that purpose, the digital image correlation (DIC) technique, which becomes a potential powerful tool to understand the detailed failure mechanism of composites, is specifically adopted to get a local strain distribution profile near the notch tip.
Ozawa, Kazumi; Kondo, Sosuke*; Nozawa, Takashi; Tanigawa, Hiroyasu; Hinoki, Tatsuya*
no journal, ,
A SiC/SiC composite is a promising material for fusion DEMO reactor. In this presentation, dimensional and microstructural stabilities of advanced SiC fibers after high-dose ion irradiation at the temperature, where the composite is to be used as a flow channel insert (FCI), were evaluated by step height measurement and FE-TEM, respectively. As a preliminary result using the step height measurement, matrix and fiber was relatively flat and had no significant gap in a Tyranno-SA3 composite after ion irradiation at 600C to 100 dpa, while in a Hi-Nicalon Type-S composite a hollow part was observed in the center of the fiber. Differences of two types of advance SiC fibers on microstructure were discussed, compared with previous neutron/ion- irradiated data, considering the issues associated with ion irradiation and effects of pyloritic carbon interphase.
Nozawa, Takashi; Tanigawa, Hisashi; Hirose, Takanori; Ozawa, Kazumi; Tanigawa, Hiroyasu; Enoeda, Mikio
no journal, ,
A hot isostatic press (HIP) process is a key technology to fabricate a first wall (FW) with cooling channels of the fusion blanket system, and development of the destructive/non-destructive inspection techniques is strongly required. Conventional Charpy impact test is a well-established test method but this technique cannot be applied to the thin-walled cooling channels of the actual component. In contrast, the authors recently proposed a brand new method utilizing a miniature torsion specimen. This study first applied this developmental technique with a miniature specimen to evaluate the HIP joint of the model blanket structure and to evaluate its mechanical properties. The test results show minor difference of the fracture energy but clearly identified that the yield and maximum strength of the HIP joint were equivalent to those of the base metal, eventually identifying the sound structural stability of the HIP joint of the model blanket structure.
Ozawa, Kazumi; Koyanagi, Takaaki*; Nozawa, Takashi; Kato, Yutai*; Kondo, Sosuke*; Tanigawa, Hiroyasu; Snead, L. L.*
no journal, ,
A silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate material for an advanced fusion DEMO blanket. High-dose irradiation experiments were performed with our special focuses on understanding; (1) integrity of the Hi-Nicalon Type-S (HNLS) composites, (2) functionality of thin pyrocarbon (PyC) /SiC multilayer, and (3) clarifying the mechanism underlying degradation, as feedback to R&D on SiC/SiC composites. The materials used in this study were plain-weave HNLS composites produced via the chemical vapor infiltration process. Neutron irradiation was conducted in the HFIR at ORNL. The peak neutron fluence was ~1.0
10
n/m
(E 
0.1 MeV, equivalent to ~100 dpa) at nominal irradiation temperatures of 300, 500, and 800C. Results of post irradiation experiments including 1/4-four-point flexural tests, SEM, and TEM observation were reported.
Hamaguchi, Dai; Tanigawa, Hiroyasu; Ozawa, Kazumi; Fujii, Hidetoshi*; Morisada, Yoshiaki*
no journal, ,
Friction-Stir Process were applied to OFCCu in order to evaluate the applicability of the process to mechanically strengthening pure-Cu and possible structural improvement on CuCrZr alloy. In this study, the tool rotational speed was varied from 50 to 500 rpm in order to clarify the effect of rotational speed on the process. The result showed the achievement of very fine grain structure at the rotational speed of 100 and 200 rpm and also the hardness increase to about 1.5 time higher within the stir-zone than that of the base metal at the most. However, the result also revealed that the rapid decrease of the hardness toward a depth direction and relatively shallow stir-zone depth compared to a length of the pin. This can be explained as post-annealing effect due to a good thermal conductivity of a pure-Cu. To avoid the effect, we are considering to introduce compulsory cooling system during the process, which application is more important to a CuCrZr alloy because more rapid cooling and lower thermal diffusion to base metal are required.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
It is being proven that fusion-grade SiC/SiC composites are featured in quasi-ductility with progressive fiber pullouts in fracture, strength anisotropy owing to variety of fabric architecture, notch insensitivity about damage tolerance, edge effect on strength and so on by failure evaluation of this class of composites. From these aspects, a unique materials standards and codes should probably be necessary for composites themselves since they are quite different from ductile metals and brittle ceramics. In this paper, a fundamental concept toward materials codes and standards development specific to the fusion-grade SiC/SiC composites and future actions will be discussed based on the recent achievements.
